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6 Replies Latest reply: Jan 22, 2013 1:24 AM by BillyVerreynne RSS

How many 11gR2 RAC instance servers would be needed?

888748 Newbie
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On the shared SAN drive - there will be as many as 6 11gR2 databases. For 2 node RAC instance servers - how many instance servers would work fine - are two separate servers needed for each database?
  • 1. Re: How many 11gR2 RAC instance servers would be needed?
    JohnWatson Guru
    Currently Being Moderated
    I think you are asking how many instances each database should have? Wrong question.

    Begin by asking whether each database should be RAC'ed at all. Don't use RAC just because you can: use it because you have proven (mathematically) that it will fix the problems you are facing. Have you defined what the problems are? Only then start thinking about how many instances. Some of your databases will be better single instance. Run them on the cluster of course (for example, so that you can take advantage of sever pooling for fault tolerance) but don't assume that RAC is the answer to everything.

    Start by defining the issues to be addressed.
  • 2. Re: How many 11gR2 RAC instance servers would be needed?
    baskar.l Pro
    Currently Being Moderated
    Hi,

    For better idea take a look at this presentation http://www.slideshare.net/MarkusMichalewicz/cloud-consolidation-with-oracle-rac-how-much-is-too-much

    baskar.l
  • 3. Re: How many 11gR2 RAC instance servers would be needed?
    Hemant K Chitale Oracle ACE
    Currently Being Moderated
    are two separate servers needed for each database?
    It depends on
    a) Whether you need RAC
    b) Whether the current database and application design will not develop bottlenecks when running in RAC

    Not every database/application needs RAC.
    Not every database/application continues to provide the same level or higher level of performance when moved to RAC.

    Hemant K Chitale

    Edited by: Hemant K Chitale on Jan 22, 2013 1:23 PM
  • 4. Re: How many 11gR2 RAC instance servers would be needed?
    BillyVerreynne Oracle ACE
    Currently Being Moderated
    To add my 2'c to the feedback provided.

    Assuming RAC is needed, then it does not make sense to run multiple db instances per server.

    RAC is about scaling a physical database by adding more servers to it. Running multiple databases per server is the exact opposite - adding more physical databases to a single server. This very seldom (if ever) makes sense.

    RAC support server pools. Which is perhaps what you should consider. You can create a cluster/grid of 10 servers and 3 server pools. Each pool runs a specific RAC database on a specific number of servers.

    E.g. pool 1 is nodes 1 to 5 and runs RAC db1. Pool 2 is nodes 6 and 7 and runs RAC db2. Pool 3 is nodes 8 to 10 and runs RAC db3. If you need more horses for db3, you can dynamically decrease pool 1 by 1 server and reassign that server to pool 3.

    This is called policy managed RAC and provides a greater level of flexibility when you want to use your cluster for running multiple databases. With an admin managed RAC, doing the same is significantly more complex and very clumsy.
  • 5. Re: How many 11gR2 RAC instance servers would be needed?
    JohnWatson Guru
    Currently Being Moderated
    Billy  Verreynne  wrote:
    RAC support server pools. Which is perhaps what you should consider. You can create a cluster/grid of 10 servers and 3 server pools. Each pool runs a specific RAC database on a specific number of servers.

    E.g. pool 1 is nodes 1 to 5 and runs RAC db1. Pool 2 is nodes 6 and 7 and runs RAC db2. Pool 3 is nodes 8 to 10 and runs RAC db3. If you need more horses for db3, you can dynamically decrease pool 1 by 1 server and reassign that server to pool 3.
    Surely in this case, Billy, you would want all ten nodes to be members of all three pools: include them all in the -n list of srvctl add srvpool for all the pools. But then each limit each pool's active membership with the -u argument, such that pool1 can have max 5 active servers and so on. Let the cluster decide which servers whould run which instances, rather than hard coding it?
  • 6. Re: How many 11gR2 RAC instance servers would be needed?
    BillyVerreynne Oracle ACE
    Currently Being Moderated
    Was intended to be a simplistic example to show that it is easy to resize pools. Makes adding new servers to the cluster, a breeze. :-)

    PS. In my case I need to hardcode it as the servers, despite same h/w model, have differences in RAM and CPU.

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